Achieving Ultra‐Low Megahertz Loss in Nanocrystalline Magnetic Powder Cores via Alloy Design and a Self‐Healing Organic–Inorganic‐Derived Hybrid Insulating Layer

ABSTRACT High‐frequency power electronics demand soft magnetic core materials with high saturation magnetic flux density ( B s ) and ultra‐low high‐frequency core loss ( P cv ) in the megahertz range. Here, we design a Fe 74.3 P 3.9 Si 7.6 B 9.5 C 1.9 Nb 2 Cu 0.8 nanocrystalline alloy with excellent soft magnetic properties and prepare fully amorphous spherical powders via gas atomization. A self‐healing organic–inorganic‐derived hybrid insulating layer composed of FePO 4 /B 2 O 3 /epoxy resin is constructed through phosphoric acid passivation followed by in situ triethyl borate (TEB) coating. During subsequent annealing, the low‐melting‐point B 2 O 3 melt heals microcracks, forming a continuous and homogeneous interfacial layer that synergistically suppresses hysteresis, eddy‐current, and excess losses. The optimized TEB‐2 magnetic powder core exhibits exceptional comprehensive performance: an ultra‐low P cv of 265 mW/cm 3 at 0.1 T and 100 kHz (8.6 W/cm 3 at 0.1 T and 1 MHz), an effective B s of 1.00 T, an effective permeability ( µ e ) of 51 at 1 MHz, and a DC‐bias of 48% at 100 Oe. Finite‑element simulations corroborate that the hybrid coating homogenizes local flux distribution and suppresses interfacial flux perturbations, directly accounting for the reduced excess loss. This work demonstrates a synergistic strategy combining alloy design and interface engineering, offering theoretical insights and experimental guidance for developing nanocrystalline magnetic powder cores for next‐generation high‐frequency power devices.